The primary thrust of this research project is to define the mechanisms responsible for the myocardial blood flow transmural distribution in dogs and pigs. Animals are to be studied with normal size hearts with left ventricular hypertrophy secondary to supravalvular aortic stenosis and mitral insufficiency. Myocardial blood flow distribution is measured with 7-10 micrometer micropheres during the awake state. To date the work has demonstrated a marked perfusion deficit distal to areas of stenosis and a similar perfusion deficit during high flow states in the hypertrophied ventricle. In addition, studies have been carried out in the normal pig, and no predilection for collateral perfusion of the epicardial layer has been found. In dogs with chronic collateral circulation, both pacing-induced tachycardia and exercise have demonstrated a marked subendocardial perfusion deficit. However, an increase during exercise in all layers was noted, indicating that exercise is associated with dilatation of the collateral circulation. Studies of the effects of nitroglycerin and propranolol have been carried out and nitroglycerin has been found to redistribute flow in the ischemic myocardium in the absence of changes in peripheral hemodynamics.